This invention relates to data buses, and more particularly to a current mode data bus having a plurality of magnetic coupler assemblies and a corresponding plurality of coupling circuits all supported on a single printed circuit board and thus forming an integrated assembly.
Present day implementations of current mode data buses typically utilize discrete magnetic coupling devices which are clamped unto unshielded portions of the data bus for each component connected to the data bus. This construction is shown in FIG. 1. The coupler assemblies xe2x80x9cCxe2x80x9d are magnetically coupled to an unshielded portion xe2x80x9cPxe2x80x9d of an external bus xe2x80x9cBxe2x80x9d. While generally satisfactory performance is obtained with this form of current mode data bus, there are some shortcomings. For example, the need to leave a portion of the external bus unshielded (i.e., partitioned) invites electromagnetic interference. As a result, such an unshielded length of conductor presents an opportunity for unwanted electromagnetic interference (EMI) emissions and is more susceptible to EMI caused by lightning, which aircraft are often exposed to. Such current mode data buses are also susceptible to varying data channel characteristics.
Accordingly, there exists a need for a current mode data bus interface apparatus which allows a plurality of magnetic coupler assemblies to be magnetically coupled to an unshielded portion of a conductor which is in communication with an existing current mode data bus, and where all of the magnetic coupler assemblies and the unshielded length of conductor are disposed on a single support structure. Such an interface assembly could itself include shielding to thus shield the unshielded portion of the conductor from electromagnetic interference. Providing all the coupler assemblies on a single interface assembly would also allow overall reduced fabrication costs of the coupler assemblies and provide for more consistent data channel characteristics.
The present invention is directed to a current mode data bus interface assembly. In one preferred embodiment the interface assembly is intended to interface with an existing current mode data bus. In an alternative preferred embodiment, the invention provides a complete current mode data bus on a circuit board assembly.
In the first preferred embodiment, a printed circuit board is provided on which is disposed a plurality of magnetic coupler assemblies. Each of the magnetic coupler assemblies are interfaced to a length of unshielded data bus. One end of the unshielded data bus is coupled to the external current mode data bus. Also disposed on the printed circuit board are a corresponding plurality of coupler circuits located adjacent to associated ones of the magnetic coupler assemblies. The magnetic couplers and coupler circuits, together with the printed circuit board, thus form an interface assembly for allowing a plurality of external devices, such as terminals, to communicate on the existing current mode data bus. This arrangement thus integrates the otherwise discrete coupler assemblies with a single support structure, as well as with each of the coupler circuits associated with the magnetic coupler assemblies. When appropriate shielding is added to the interface assembly, the unshielded length of data bus on the printed circuit board is much less susceptible to EMI. Data channel characteristics are also proved because of the uniformity of construction of the magnetic coupler assemblies and the coupler circuits.
In an alternative preferred embodiment, the entire current mode data bus is provided on the printed circuit board and terminated at each end with suitable terminators. An unshielded portion of the current mode data bus extends between the terminators. Magnetic coupler assemblies magnetically couple the unshielded portion of the data bus to associated coupler circuits. This embodiment also provides the advantages of reducing EMI on the unshielded portion of the data bus as well as establishing more consistent data channel characteristics.
Further areas of applicability of the present invention will become apparent from the detailed description provided hereinafter. It should be understood that the detailed description and specific examples, while indicating the preferred embodiment of the invention, are intended for purposes of illustration only and are not intended to limit the scope of the invention.